This invention relates to a contact material for a vacuum switch, to a method of manufacture.
The characteristics required of a vacuum switch contact material include superior circuit breaking performance, high withstanding voltage, a small chopping current, low welding separation force (which means a force required for pulling apart both contacts melted together by means of current) and low wear. A material which satisfies all of these characteristics has however, still not been developed, and some of these characteristics have to be sacrificed depending on the intended application under the present conditions.
Cu--Cr contact materials, for example, have excellent circuit breaking performance and withstand voltage, and so they are used mainly for vacuum circuit breakers, however as they have a high chopping current, they are not very suitable for motor switches. Also, they have a rather high welding separation force, so that considerable force has to be exerted on the circuit breaker side. Ag--WC contact materials, on the other hand, have a small chopping current and are therefore used in vacuum switches for motors, but they have inferior circuit breaking performance and are not very suitable as circuit breakers.
The characteristics of contacts therefore depend on the materials of which they consist, but their characteristics may also vary according to the method of the their manufacture. For example, Cu--Cr contact materials manufactured by the sintering method show peak circuit breaking performance when the Cr content is near 25% by weight, bu if manufactured by the infiltration method, they show peak performance when the Cr content is near 45% by weight.
Conventional vacuum switch contact materials, therefore, were not satisfactory with respect to all characteristics, and some characteristics had to be sacrificed in order to fit a specific application. A contact material was therefore desired which could offer some improvement in the above-described characteristics, even if only slight.
The inventors also discovered contact materials with excellent circuit breaking performance and anti-weld property, which consists of Cu (main component), a secondary component such as Mo, and metal oxides such as Ta.sub.2 O.sub.5, and already filed a patent claim for them (Japanese Patent Application Laid-Open No. 1984-215621). Even these materials were however, unsatisfactory since as a stable, low chopping current could not be obtained. This was probably due to the effect of the secondary material, and some improvement was desired.